The inner ear disorders of hearing and balance that affect over 30 million Americans can be caused by a variety of factors including damage to mechanosensory hair cells, developmental abnormalities, and genetic mutations. Proposed research aims to gain an integrated view of mechanisms that underlie inner ear development by means of anatomical, physiological, and genetic approaches. The Xenopus acoustico-vestibular system will be used to investigate sensory endorgan formation with the long term goal of understanding how hair cells of the inner ear differentiate and acquire their unique structural and functional phenotypes during development. The experimental approach will leverage the augmented potential of Xenopus laevis and Xenopus (Silurana) tropicalis for developmental and genetic studies due to national resource sharing initiatives and genome sequencing efforts. A key objective of this research is to determine how developmental regulation of ion channel gene expression confers the distinctive electrical phenotypes that typify hair cells of auditory and vestibular endorgans. The specific aims are: (1) to compare the structural and genetic development of auditory and vestibular endorgans, (2) to determine genetic regulation of ion channel expression during inner ear development, (3) to characterize the development of the electrical phenotype of mechanosensory hair cells, and (4) to investigate hair cell differentiation and regeneration in vitro using an immature (larval) inner ear culture preparation. Anatomical and molecular data gathered as part of this research will be prepared for dissemination in the public domain via online databases. The experimental plan will incorporate diverse methods including immunohistochemistry, multiphoton and confocal microscopy, electrophysiology (patch clamp), RT-PCR, molecular cloning, yeast two hybrid analysis, transient transfection, and cell culture. As part of this effort, putative promoter sequences for ion channels will be cloned and used to produce transgenic Xenopus lines. Experimental results are intended to advance fundamental understanding of mechanosensory hair cell differentiation during organogenesis, and of the genetic control of acoustico-vestibular development. Results of these investigations also may be valuable in design of treatments for hereditary and environmentally-induced sensory disorders of hearing and balance.